Measuring diversity patterns with urbanization

Dragonfly exuviae were sampled from lentic wetlands in natural, suburban, and urban areas of Rhode Island, USA.  We found no relationship between species richness and urbanization (characterized by surrounding forest habitat and chloride concentration at each wetland).  To further analyze diversity patterns along the urbanization gradient, we evaluated five other measures—two diversity indices and three measures of evenness. Urban sites are thought to have few species and low evenness relative to undisturbed sites.  However, none of the measures of diversity or evenness of the dragonfly faunas was correlated with degree of urbanization.  One of our measures of evenness was a novel approach that used the slope of a log-log dominance-diversity curve as a direct, empirical measure.  This slope is the only one of the five measurements that is completely unrelated to species richness. The log-log slope of dominance-diversity is therefore a potentially valuable way of measuring evenness, independent of species richness, when evaluating species diversity of natural communities.